The incidence of testicular germ cell tumors (TGCT) has doubled in the past 40 years. An annual increase of 3[unreadable]6% is reported for Caucasian populations.Testicular cancer is the most common malignancy affecting males aged 14-40 and accounting for up to 60% of all malignancies diagnosed at this age. Despite a high cure rate, they represent the most frequent cause of death from solid tumors in this age group. In addition to oncogene activation, the inactivation of tumor suppressor genes (TSGs) has been shown to play an important role in tumorigenesis. According to the revised Knudson's two-hit hypothesis, full inactivation of a tumor suppressor gene (TSGs) often involves two genetic or epigenetic events: 1) the loss or recombination of large chromosomal DNA regions containing one parental allele and a localized mutational event inactivating the second allele 2) localized mutation in one allele and methylation in another allele 3) LOH in one allele and methylation in another allele 4) biallelic methylation. We have recently discovered several cancer specific methylated genes by a robust approach that couples probabilistic search algorithms with the pharmacologic unmasking strategy for unbiased and precise global localization of tumor-specific methylated genes. We also validated a highthroughput assay for more than 50 genes (QMSP, quantitative methylation specific PCR) for robust analysis of several types of cancer with high sensitivity and specificity. In parallel, we have pioneered the use of single nucleotide polymorphism (SNP) arrays for analyzing cancer loss-of-heterozygosity (LOH) and performed a proof of principal study using SNP based arrays for the diagnosis of bladder cancer in urine sediment. We now propose the following aims: 1. To analyze patterns of chromosomal loss in testicular cancers from different stages using single nucleotide polymorphism (SNP) array hybridization of over 10,000 markers 2. To discovery of testicular cancer specific methylated genes by a robust approach that couples probabilistic search algorithms in the entire human genome with an established pharmacologic unmasking strategy in cancer cell lines. 3. To compare the genomic and epigenomic patterns in different stages of testicular cancer After carrying our first 2 specific aims, we will identify the gene or genes in a critical area of genetic and epigenetic alterations involved in testicular cancer. In addition, identification of these area and comparison of genetic and epigenetic alterations will shed important light on the biology of testicular cancer progression. Functional studies may provide insights into the first steps of germ cell immortilization and subsequent progression in cancer. Ultimately, SNP markers and methylation markers may lead to new diagnostic, monitoring and therapeutic approaches in testicular cancer. In addition this comprehensive analysis will lead us to understand the biology of testicular cancer development.